It is known that the skin of an individual continuously breathes and perspires, perspiration becoming more abundant as body activity and its temperature increase, especially during and following activity.
When skin is naked, sweat resulting from this perspiration is vaporized into the ambient air, thereby promoting cooling of the skin surface and thermal regulation of the body.
When the skin is covered, for example with an article of clothing, vaporization of sweat, as well as the corresponding heat exchange, occurs only to a limited extent. The skin becomes moist, the moisture is more or less absorbed by the material covering the skin, and this material becomes wet to a corresponding degree, thereby causing well-known, disagreeable sensations.
This discomfort becomes especially pronounced when the material covering the skin is moisture-proof and in particular moisture-proof to water-proof, since the moisture thus produced cannot be channelled away to the outside and remains in contact with the skin, thus producing an uncomfortable feeling.
Furthermore, in the case of an article of clothing designed to protect against cold, the undrained moisture thus produced conducts cold and is a factor leading to cooling of the skin.
In-the case of sports clothing which both insulates and provides moisture-proofing, since it is subjected to marked variations of temperature between the outer surface and the skin which vary over time as a function of the activity of the individual, the moisture-proofing can increase still further, and in pronounced fashion, the feeling of discomfort.
In fact, perspiration, composed mainly of water, is a good conductor of heat. In the event of insufficient thermal insulation, the sweat thus cools very rapidly and condenses, a phenomenon which exacerbates the feeling of discomfort. Moreover, a "soaked" insulator loses the major portion of its thermal insulation qualities.